I'm sure this has been asked before, but I can't find it, and it's not in the FAQ (it should be - please!)

On which samples is --alt-preset extreme audibly better than --alt-preset standard.On which samples is --alt-preset insane audibly better than --alt-preset extreme.On which samples is --alt-preset insane not transparent?

JohnV did say exactly that, but Dibrom said "and by specifying -Z you may end up degrading quality in cases as well."

I can't figure out if he had any specific for saying this, because it came in one of the (at the time) very frequent replies which essentially said "Look, don't worry about the switches which are in --alt-preset standard, because there are things which can't be accessed from the command line; and don't try to improve it by adding other switches, because it's already as good as it can get, and more importantly, you'll almost certainly make it worse by trying to 'tweak' it".

So maybe he had a very specific problem in mind, or maybe he was just trying to stop people messing with the --alt-presets.